Spinal fixation, such as lumbar sacral fusion and the correction of spinal deformities such as scoliotic curves, is a well known and frequently used medical procedure. Pedicle, lateral, and oblique mounting means may be used to secure corrective spinal instrumentation to a portion of the spine that has been selected to be fused by arthrodesis.
A spinal fixation system comprises corrective spinal instrumentation that is attached to selected vertebrae of the spine by screws, hooks, and clamps. The corrective spinal instrumentation comprises spinal rods or plates, which are generally parallel to the patient's back. The corrective spinal instrumentation further comprises connecting rods, which extend from the spinal rods or plates. Spinal fixation systems are used to correct problems in the lumbar and thoracic portions of the spine, and are often installed posterior to the spine on opposite sides of the spinous process and adjacent to the transverse process.
Various types of screws, hooks, and clamps have been used for attaching corrective spinal instrumentation to selected portions of a patient's spine. Examples of pedicle screws and other types of attachments are shown in U.S. Pat. Nos. 4,763,644; 4,805,602; 4,887,596; 4,950,269; and 5,129,388. These patents are incorporated by reference for all purposes within this application.
Spinal fixation systems often require that the connecting rods be maintained at a certain fixed angle with the spinal rods or plates that make up the corrective spinal instrumentation. The spinal rods or plates that comprise the corrective spinal instrumentation are often generally parallel to the patient's back. The angle that each connecting rod makes with the attached vertebra may change only slightly during treatment. Additionally, the angle that a connecting rod makes with a vertebra may vary from person to person due to the unique anatomical structure of each patient. As a result, prior devices tend to comprise blocks and screws produced with various unchangeable angles to enable a physician to couple the corrective spinal instrumentation to the connecting rods while accommodating the initial placement of the connecting rods with the patient's vertebra. Therefore, large sets of components may be necessary to accommodate the many significant anatomical variations from person to person.
Some prior devices may accommodate a limited number of different placements of the connecting rods in the patient's vertebrae. Yet these devices often require a different set of components for each of the specified angles. In addition, such prior devices are often limited to fixed angles in increments of five degrees, such as 0.degree., 5.degree., and 10.degree..